Inorganic-organic compounds obtained by placing an organic compound between layers of inorganic layered material have the potential to demonstrate characteristics that cannot be achieved by an individual host or guest, due to the interaction of the inorganic and organic layer. Layered double hydroxides (hereinafter referred to as LDH) represented by hydrotalcite are the host material of hope, because they have characteristics not found in other layered materials, such as, the anion can be placed in between layers and it can be synthesized under relatively non-severe conditions. (Makoto Ogawa, et al. “Surface”, 32 (11), 695, (1994)).
These intercalation compounds that are obtained through intercalation in which the guest material is inserted between layers of inorganic layered material are inorganic-organic nano double materials that have a structure such that a nanometer order of thickness of the host layers and guest layers are alternately laminated. The guest exists in the two-dimensional nano-space called the intercalation, and it has a distinctive state due to the interaction between the host-guest or guest-guest. In addition to the basic scientific interest in these interactions and micro-structures that are derived from such development in this area of material design has attracted a great deal of attention. A wide range of potential, such as, as an absorbent, catalyst, ion exchange material, and ion conductor has already been pointed out. (Makoto Ogawa “Catalyst”, 39 (7), 557, (1997)).
The LDH having an anion in between the layers demonstrates characteristics that other layered materials do not have. Therefore, the synthesis of LDH intercalation compounds using an organic anion as the guest has been investigated using such techniques as the coprecipitation method, the ion exchanging method, and the reconstruction method. As an organic acid guest compound, surfactants such as an alkyl sulfate or a fatty acid, aromatic hydrocarbon carboxylic acid compounds such as phthalic acid or benzoic acid, and pigment compounds such as indigo carmine are known.
Deoxycholic acid (hereinafter referred to as DCA) is one of the bile acids and a surfactant that carries cholesterols in organisms. Its association state is still unclear and the structure of layered compounds using this as a guest is very interesting.
Therefore, the present inventors attempted the synthesis of a deoxycholic acid-layered double hydroxide intercalation compound (LDH-DCA layered compound) using coprecipitation and the ion exchanging method. However, with these methods of the prior art, it was difficult to place the DCA in between the layers. It was assumed that the difficulty is due to the DCA being sterically complicated and having a large size so that the selectivity of the ion exchange is low and it is hindered by the coexisting anions.